Tire

ABSTRACT

In a tire, first and second center land portions each include a circumferential narrow groove and first and second lateral grooves. The first and second lateral grooves of the first center land portion are disposed overlapped with each other in a tire circumferential direction. The first and second lateral grooves of the second center land portion are disposed overlapped with each other in the tire circumferential direction. The first and second lateral grooves of the first center land portion are disposed offset with respect to the first and second lateral grooves of the second center land portion in the tire circumferential direction.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority pursuant to 35 U.S.C. 119(a) toJapanese Patent Application No. 2021-157532, filed Sep. 28, 2021, whichapplication is incorporated herein by reference in its entirety.

TECHNICAL FIELD

The technology relates to a tire and particularly relates to a tire thatcan provide wet braking performance, uneven wear resistance performance,and noise performance in a compatible manner.

BACKGROUND ART

To provide wet performance and uneven wear resistance performance of atire in a compatible manner, a configuration in which a center landportion includes a circumferential narrow groove and narrower lateralgrooves has recently been employed. The technology described in JapanUnexamined Patent Publication No. 2007-326433 is a conventional tireemploying such a configuration.

SUMMARY

The technology provides a tire that can provide wet braking performance,uneven wear resistance performance, and noise performance in acompatible manner.

A tire according to an aspect of the technology includes a pair ofshoulder main grooves and one or more center main grooves and a pair ofshoulder land portions and two or more center land portions defined andformed by the shoulder main grooves and the center main grooves. Of thetwo or more center land portions, a first center land portion adjacentto a shoulder land portion of the pair of shoulder land portions and asecond center land portion adjacent to the first center land portion aredefined. The first and second center land portions each include acircumferential narrow groove extending in a tire circumferentialdirection, a first lateral groove opening to one edge portion of thecenter land portion at one end and connecting to the circumferentialnarrow groove at the other end, and a second lateral groove opening tothe other edge portion of the center land portion at one end andconnecting to the circumferential narrow groove at the other end. Thefirst and second lateral grooves of the first center land portion aredisposed overlapped with each other in the tire circumferentialdirection, the first and second lateral grooves of the second centerland portion are disposed overlapped with each other in the tirecircumferential direction, and the first and second lateral grooves ofthe first center land portion are disposed offset with respect to thefirst and second lateral grooves of the second center land portion inthe tire circumferential direction.

In the tire according to an aspect of the technology, (1) the first andsecond center land portions each include the circumferential narrowgroove and the lateral grooves, improving drainage properties of thetread portion center region. Further, (2) the first and second lateralgrooves are disposed overlapped with each other in the tirecircumferential direction in each of the first and second center landportions, and the concentration of distortion on the edge portionsdefined by the lateral grooves is relieved. Thus, uneven wear of thecenter land portions is suppressed compared with a configuration wherethe lateral grooves are disposed offset in the tire circumferentialdirection. Furthermore, (3) the lateral grooves of the adjacent centerland portions are disposed mutually offset in the tire circumferentialdirection. Accordingly, as compared with a configuration where thelateral grooves of the adjacent center land portions are disposedoverlapped in the tire circumferential direction, periodic resonancecaused by the lateral grooves is canceled, and noise during traveling isreduced. This has the advantage of providing wet performance, unevenwear resistance performance, and noise performance in a compatiblemanner.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a cross-sectional view in a tire meridian directionillustrating a tire according to an embodiment of the technology.

FIG. 2 is a plan view illustrating a tread surface of the tireillustrated in FIG. 1 .

FIG. 3 is an enlarged view illustrating center land portions illustratedin FIG. 2 .

FIG. 4 is an enlarged view illustrating one of the center land portionsillustrated in FIG. 3 .

FIG. 5 is an enlarged view illustrating a circumferential narrow grooveand lateral grooves of the center land portion illustrated in FIG. 4 .

FIG. 6 is a cross-sectional view of the center land portion illustratedin FIG. 4 .

FIG. 7 is a cross-sectional view illustrating the center land portionillustrated in FIG. 4 .

FIG. 8 is a cross-sectional view illustrating an edge portion of ashoulder land portion illustrated in FIG. 2 .

FIG. 9 is a plan view illustrating a modified example of the tireillustrated in FIG. 2 .

FIG. 10 is a table indicating the results of performance tests of tiresaccording to embodiments of the technology.

FIG. 11 is a table indicating the results of performance tests of tiresaccording to embodiments of the technology.

FIG. 12 is a plan view illustrating a tread surface of a tire ofConventional Example.

DETAILED DESCRIPTION

Embodiments of the technology will be described in detail below withreference to the drawings. Note that the technology is not limited tothe embodiments. Additionally, constituents of the embodiments includeconstituents that are substitutable and are obviously substitutes whilemaintaining consistency with the embodiments of the technology.Additionally, a plurality of modified examples described in theembodiments can be combined in a discretionary manner within the scopeof obviousness to one skilled in the art.

Tire

FIG. 1 is a cross-sectional view in a tire meridian directionillustrating a tire 1 according to an embodiment of the technology. Thesame drawing illustrates a cross-sectional view of a half region in atire radial direction. In this embodiment, a heavy duty pneumatic radialtire mounted on a long-distance transport vehicle such as a truck or buswill be described as an example of the tire.

In the same drawing, a cross-section in the tire meridian direction isdefined as a cross-section of the tire taken along a plane that includesa tire rotation axis (not illustrated). Additionally, a tire equatorialplane CL is defined as a plane that passes through a midpoint of a tirecross-sectional width specified by the Japan Automobile TyreManufacturers Association Inc. (JATMA) and that is perpendicular to thetire rotation axis. Additionally, a tire width direction is defined as adirection parallel to the tire rotation axis, and the tire radialdirection is defined as a direction perpendicular to the tire rotationaxis.

The tire 1 includes an annular structure with the tire rotation axisbeing as the center, and includes a pair of bead cores 11, 11, a pair ofbead fillers 12, 12, a carcass layer 13, a belt layer 14, a tread rubber15, a pair of sidewall rubbers 16, 16, and a pair of rim cushion rubbers17, 17 (see FIG. 1 ).

The pair of bead cores 11, 11 each include one or more of bead wiresmade of steel and made by being wound annularly multiple times, and thepair of bead cores 11, 11 are embedded in bead portions and constitutecores of the bead portions of left and right. The pair of bead fillers12, 12 are each made of a lower filler 121 and an upper filler 122. Thepair of bead fillers 12, 12 are disposed in outer circumferences in thetire radial direction of the pair of bead cores 11, 11, respectively,and reinforce the bead portions.

The carcass layer 13 includes a single layer structure made of onecarcass ply, or a multilayer structure made of a plurality of carcassplies being layered, and the carcass layer 13 extends in a toroidalshape between the bead cores 11, 11 of left and right, and constitutesthe backbone of the tire. Additionally, both end portions of the carcasslayer 13 are wound and turned back toward an outer side in the tirewidth direction to wrap the bead cores 11 and the bead fillers 12 andare fixed. Additionally, the carcass ply of the carcass layer 13 isconstituted by covering, with coating rubber, a plurality of carcasscords made of steel and by performing a rolling process on the carcasscords. The carcass ply of the carcass layer 13 has a cord angle (definedas an inclination angle in a longitudinal direction of the carcass cordswith respect to a tire circumferential direction) of 80 degrees or moreand 90 degrees or less as an absolute value for a radial tire and 30degrees or more and 45 degrees or less for a bias tire.

The belt layer 14 is made of a plurality of belt plies 141 to 144 beinglayered and is disposed around an outer circumference of the carcasslayer 13. The belt plies 141 to 144 include a large-angle belt 141, apair of cross belts 142, 143, and a belt cover 144. The large-angle belt141 is constituted by covering, with coating rubber, a plurality of beltcords made of steel and by performing a rolling process on the beltcords. The large-angle belt 141 has a cord angle (defined as aninclination angle in a longitudinal direction of the belt cords withrespect to the tire circumferential direction) of 45 degrees or more and70 degrees or less as an absolute value. The pair of cross belts 142,143 are each constituted by covering, with coating rubber, a pluralityof belt cords made of steel and by performing a rolling process on thebelt cords. Each of the pair of cross belts 142, 143 has a cord angle of10 degrees or more and 55 degrees or less as an absolute value.Additionally, the pair of cross belts 142, 143 have cord angles havingmutually opposite signs, and the pair of cross belts 142, 143 arelayered by making the belt cords mutually intersect in the longitudinaldirection of the belt cords (a so-called crossply structure is formed).The belt cover 144 is constituted by covering, with coating rubber, aplurality of belt cover cords made of steel or an organic fiber materialand by performing a rolling process on the belt cover cords. The beltcover 144 has a cord angle of 10 degrees or more and 55 degrees or lessas an absolute value.

The tread rubber 15 is disposed on an outer periphery in the tire radialdirection of the carcass layer 13 and the belt layer 14 and constitutesa tread portion of the tire 1. The pair of sidewall rubbers 16, 16 aredisposed on an outer side in the tire width direction of the carcasslayer 13 and constitute sidewall portions of left and right,respectively. The pair of rim cushion rubbers 17, 17 extend from aninner side in the tire radial direction of the bead cores 11, 11 of leftand right and turned back portions of the carcass layer 13 toward theouter side in the tire width direction and constitute rim fittingsurfaces of the bead portions.

Tread Surface

FIG. 2 is a plan view illustrating a tread surface of the tire 1illustrated in FIG. 1 . The same drawing illustrates a tread surface ofan all-season tire. In the same drawing, “tire circumferentialdirection” refers to the direction about the tire rotation axis.Additionally, reference sign T denotes a tire ground contact edge, anddimension symbol TW denotes a tire ground contact width.

As illustrated in FIG. 2 , the tire 1 includes, in the tread surface,four circumferential main grooves 21, 22 and five land portions 31 to33.

The circumferential main grooves 21, 22 include a pair of shoulder maingrooves 21, 21 and two center main grooves 22, 22. The circumferentialmain grooves 21, 22 each have an annular structure continuouslyextending along the entire circumference of the tire. The shoulder maingrooves 21, 21 are circumferential main grooves located on the outermostside in the tire width direction of the plurality of circumferentialmain grooves 21, 22 and are defined respectively by left and rightregions between which the tire equatorial plane CL form the boundary.The center main groove 22 is defined as a circumferential main groovefurther on the tire equatorial plane CL side than the shoulder maingroove 21.

“Main groove” refers to a groove on which a wear indicator must beprovided as specified by JATMA.

Further, the shoulder main groove 21 has a groove width Wg1 (see FIG. 2) of 8.0 mm or more and 13.0 mm or less and a groove depth Hg1 (see FIG.7 described below) of 12.0 mm or more and 16.5 mm or less. Furthermore,the center main groove 22 has a groove width Wg2 (see FIG. 2 ) of 3.5 mmor more and 13.0 mm or less and a groove depth Hg2 (see FIG. 7 describedbelow) of 12.0 mm or more and 16.5 mm or less. Additionally, the groovewidth Wg2 of the center main groove 22 with the groove width Wg1 of theshoulder main groove 21 is in the range 0.14≤Wg2/Wg1≤1.00.

The groove width is measured as a maximum value of a distance betweenopposed groove walls of a groove opening portion on the tread contactsurface when the tire is mounted on a specified rim, inflated to aspecified internal pressure, and in an unloaded state. In aconfiguration in which the groove opening portion includes a notchportion or a chamfered portion, the groove width is measured by using,as end points, intersection points of an extension line of a treadcontact surface and extension lines of the groove walls, in across-sectional view parallel to a groove width direction and a groovedepth direction.

The groove depth is measured as the maximum value of a distance from thetread contact surface to the groove bottom when the tire is mounted on aspecified rim, inflated to the specified internal pressure, and in anunloaded state. Additionally, in a configuration in which a groovebottom includes partial recess/projection portions or a sipe, the groovedepth is measured excluding the partial recess/projection portions orthe sipe.

“Specified rim” refers to a “standard rim” defined by JATMA, a “DesignRim” defined by the Tire and Rim Association, Inc. (TRA), or a“Measuring Rim” defined by the European Tyre and Rim TechnicalOrganisation (ETRTO). Additionally, “specified internal pressure” refersto a “maximum air pressure” defined by JATMA, the maximum value in “TIRELOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES” defined by TRA, or“INFLATION PRESSURES” defined by ETRTO. Additionally, “specified load”refers to a “maximum load capacity” defined by JATMA, the maximum valuein “TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES” defined byTRA, or “LOAD CAPACITY” defined by ETRTO. However, in JATMA, in the caseof a tire for a passenger vehicle, specified internal pressure is an airpressure of 180 kPa, and specified load is 88% of the maximum loadcapacity at the specified internal pressure.

Also, in the configuration of FIG. 2 , a distance (dimension symbolomitted in drawings) from the tire equatorial plane CL to a groovecenter line of each of the left and right shoulder main grooves 21, 21is in the range of 26% or more and 32% or less of a tire ground contactwidth TW.

The groove center line is defined as an imaginary line connectingmidpoints of a distance between groove walls opposed to each other.

The tire ground contact width TW is measured as a maximum lineardistance in a tire axial direction in a contact surface between the tireand a flat plate when the tire is mounted on a specified rim, inflatedto a specified internal pressure, placed perpendicular to the flat platein a static state, and subjected to a load corresponding to a specifiedload.

A tire ground contact edge T is defined as the maximum width position ina tire axial direction on the contact surface between the tire and aflat plate when the tire is mounted on a specified rim, inflated to aspecified internal pressure, placed perpendicular to the flat plate in astatic state, and subjected to a load corresponding to a specified load.

The land portions 31 to 33 include a pair of shoulder land portions 31and 31 and three center land portions 32, 33, and 32. The land portions31 to 33 are defined and formed by the circumferential main grooves 21,22, and each of the land portions forms an annular road contact surfacethat extends along the entire circumference of the tire. The shoulderland portion 31 is defined as a land portion defined by the shouldermain groove 21 and located on the outer side in the tire widthdirection. Additionally, the pair of shoulder land portions 31, 31 aredisposed in the left and right regions between which the tire equatorialplane CL lies as a boundary. The center land portions 32, 33 are definedas land portions located between the pair of shoulder land portions 31,31.

Further, in FIG. 2 , a ground contact width Wb1 of the shoulder landportion 31 with respect to the tire ground contact width TW is in therange 0.15≤Wb1/TW≤0.25 and is preferably in the range 0.18≤Wb1/TW≤0.22.Further, a ground contact width Wb2 of the center land portion 32 and aground contact width Wb3 of the center land portion 33 with respect tothe tire ground contact width TW are respectively in the range0.13≤Wb2/TW≤0.16 and in the range 0.13≤Wb3/TW≤0.16. Additionally, theground contact width Wb2 of the center land portion 32 and the groundcontact width Wb3 of the center land portion 33 with respect to theground contact width Wb1 of the shoulder land portion 31 arerespectively in the range 0.70≤Wb2/Wb1≤0.85 and in the range0.70≤Wb3/Wb1≤0.85. In such a configuration, the shoulder land portion 31has a wide structure, and thus the rigidity of the shoulder land portion31 is ensured, and uneven wear of the shoulder land portion 31 iseffectively suppressed.

The ground contact width of the land portion is measured as a maximumlinear distance in the tire axial direction in a contact surface betweenthe land portion and a flat plate when the tire is mounted on aspecified rim, inflated to a specified internal pressure, placedperpendicular to the flat plate in a static state, and loaded with aload corresponding to a specified load.

Further, in the configuration of FIG. 2 , the tire 1 includes the pairof shoulder main grooves 21, 21 and the two center main grooves 22, 22as described above, and thus the pair of shoulder land portions 31, 31and the three center land portions 32, 33 are defined. However, no suchlimitation is intended, and the tire 1 may include one or three or morecenter main grooves (not illustrated). In the former configuration, apair of center land portions are defined, and in the latterconfiguration, four or more center land portions are defined.Additionally, the center land portion 33 may be disposed on the tireequatorial plane CL (see FIG. 2 ) or may be disposed at a position awayfrom the tire equatorial plane CL (not illustrated).

Zigzag Shape of Groove Bottom of Main Groove

Further, in the configuration of FIG. 2 , the shoulder main groove 21and the center main groove 22 each include an edge portion having astraight shape in a groove opening portion. Meanwhile, each of the maingrooves 21, 22 may have a straight shape in a groove bottom portion ormay have a zigzag shape (not illustrated). For example, the grooveopening portion of the main groove 21, 22 has a straight shape, and thegroove bottom portion has a zigzag shape. Preferably, a groove wallsurface of the main groove 21, 22 is formed of a bent surface connectingthe groove opening portion and the groove bottom portion (notillustrated). In such a configuration, an inclination angle (a so-calledgroove wall angle) of the groove wall of the main groove 21, 22 withrespect to the tread contact surface varies toward the tirecircumferential direction due to the aforementioned bent surface. As aresult, drainage properties of the main grooves 21, 22 are improved, andthe rigidity of the land portions 31 to 33 is ensured.

Center Land Portion

FIG. 3 is an enlarged view illustrating the center land portions 32, 33illustrated in FIG. 2 . FIG. 4 is an enlarged view illustrating onecenter land portion 32 (33) illustrated in FIG. 3 . FIG. 5 is anenlarged view illustrating a circumferential narrow groove 41 andlateral grooves 42A, 42B of the center land portion 33 (32) illustratedin FIG. 4 . FIGS. 6 and 7 are each a cross-sectional view illustratingthe center land portion 32 (33) illustrated in FIG. 4 . In thesedrawings, FIG. 6 illustrates a cross-sectional view along thecircumferential narrow groove 41, and FIG. 7 illustrates across-sectional view along the lateral grooves 42A, 42B.

As illustrated in FIGS. 2 and 3 , the center land portions 32, 33 eachinclude the single circumferential narrow groove 41 and a plurality oflateral grooves 42A, 42B.

As illustrated in FIG. 2 , the circumferential narrow groove 41 is anarrow groove that extends in the tire circumferential direction andincludes an annular structure continuously extending along the entirecircumference of the tire. Further, as illustrated in FIG. 3 , a groovecenter line (not illustrated) of the circumferential narrow groove 41 isdisposed in the central portion of the center land portion 32 (33).Specifically, a distance from one edge portion of the center landportion 32 (33) to the groove center line of the circumferential narrowgroove 41 with respect to the ground contact width Wb2 (Wb3) of thecenter land portion 32 (33) is in the range of 30% or more and 70% orless.

Furthermore, in FIG. 4 , a groove width Ws of the circumferential narrowgroove 41 is in the range 0.1 mm≤Ws≤2.0 mm, and is preferably in therange 0.5 mm≤Ws≤1.5 mm. Additionally, in FIG. 6 , a groove depth Hs ofthe circumferential narrow groove 41 with respect to the groove depthHg1 of the shoulder main groove 21 is in the range 0.05≤Hs/Hg1≤0.80 andis preferably in the range 0.10≤Hs/Hg1≤0.65. With the upper limitdescribed above, drainage properties of the circumferential narrowgroove 41 are ensured. With the lower limit described above, a decreasein rigidity of the center land portions 32, 33, which is caused by thearrangement of the circumferential narrow groove 41 is suppressed. Notethat the groove width Ws and the groove depth Hs of the circumferentialnarrow groove 41 may be increased or decreased in a predetermined regionas described below (see FIG. 6 ) or may be constant throughout theentire circumference of the tire (not illustrated).

Further, as illustrated in FIG. 3 , the circumferential narrow groove 41has a zigzag shape formed by alternately connecting long portions andshort portions. Furthermore, the long portion and the short portion areinclined in mutually opposite directions with respect to the tirecircumferential direction. Additionally, a maximum amplitude As of thezigzag shape with respect to the ground contact width Wb2 of the centerland portion 32 is in the range 0.05≤As/Wb2≤0.20 and is preferably inthe range 0.10≤As/Wb2≤0.15. With the lower limit described above, theeffect of improving drainage properties by the zigzag shape of thecircumferential narrow groove 41 is ensured. With the upper limitdescribed above, the rigidity of the center land portions 32, 33 isensured.

The maximum amplitude As of the zigzag shape is measured as the maximumamplitude of the groove center line of the circumferential narrow groove41.

For example, in the configuration illustrated in FIG. 4 , as illustratedin FIG. 3 , the circumferential narrow groove 41 has a zigzag shapeformed by repeatedly connecting a first long portion 411A, a first shortportion 412A, a second long portion 411B, and a second short portion412B. Additionally, the first and second long portions 411A, 411B areinclined in one direction with respect to the tire circumferentialdirection, and the first and second short portions 412A, 412B areinclined in other directions with respect to the tire circumferentialdirection.

Further, in FIG. 4 , an amplitude As1 of the zigzag shape in the firstshort portion 412A with respect to an amplitude As2 of the zigzag shapein the second short portion 412B is in the range 0.10≤As1/As2≤0.90 andis preferably in the range of 0.40≤As1/As2≤0.60. Accordingly, the zigzagshape has the small amplitude As1 in the first short portion 412A andhas the large amplitude As2 (As1<As2) in the second short portion 412B.With the lower limit described above, the effect of improving drainageproperties by the first short portion 412A is ensured. With the upperlimit described above, the rigidity of the center land portions 32, 33is ensured. Note that in the configuration of FIG. 4 , the amplitude As2of the zigzag shape in the second short portion 412B corresponds to themaximum amplitude As of the zigzag shape of the circumferential narrowgroove 41.

Furthermore, in FIG. 4 , a pitch length Ps of the zigzag shape formed ofthe first long portion 411A, the first short portion 412A, the secondlong portion 411B, and the second short portion 412B with respect to theground contact width Wb2 (Wb3) of the center land portion 32 (33) is inthe range 0.50≤Ps/Wb2≤1.10 and is preferably in the range of0.75≤Ps/Wb2≤0.95. With the lower limit described above, the effect ofimproving drainage properties by the zigzag shape of the circumferentialnarrow groove 41 is ensured. With the upper limit described above, therigidity of the center land portions 32, 33 is ensured. Additionally, anextension distance Ps' in the tire circumferential direction of a set ofthe long portion and the short portion 411A, 412A (411B, 412B) adjacentto each other with respect to the pitch length Ps of the zigzag shapeformed of the first long portion 411A, the first short portion 412A, thesecond long portion 411B, and the second short portion 412B is in therange 0.30≤Ps′/Ps≤0.70 and is preferably in the range 0.40≤Ps′/Ps≤0.60.

The extension distance Ps' in the tire circumferential direction of thefirst long portion 411A and the first short portion 412A is measuredwith bend points having the zigzag shape regarded as end points.

Further, in FIG. 4 , an inclination angle θs1 of the first and secondlong portions 411A, 411B with respect to the tire circumferentialdirection is in the range 3 degrees≤θs1≤17 degrees and is preferably inthe range 8 degrees≤θs1≤12 degrees.

The inclination angle is measured as an angle formed by a virtualstraight line connected to end points of each of the first and secondlong portions 411A, 411B, and the tire equatorial plane CL.

Also, an extension length of each of the first and second long portions411A, 411B in the tire circumferential direction (dimension symbolomitted in the drawings) with respect to the extension distance Ps' inthe tire circumferential direction of the aforementioned set of the longportion and the short portion 411A, 412A (411B, 412B) adjacent to eachother is in the range of 70% or more and 95% or less and is preferablyin the range of 80% or more and 90% or less.

Furthermore, in FIG. 4 , an inclination angle θs 2A of the first shortportion 412A with respect to the tire circumferential direction ispreferably in the range 20 degrees≤θs2A≤50 degrees and is preferably inthe range 35 degrees≤θs2A≤45 degrees. In addition, an inclination angleθs2B of the second short portion 412B with respect to the tirecircumferential direction is preferably in the range 40 degrees≤θs2B≤80degrees and is preferably in the range 55 degrees≤θs2B≤75 degrees. Also,the inclination angle θs 2B of the second short portion 412B withrespect to the tire circumferential direction with respect to theinclination angle θs2A of the first short portion 412A is in the range10 degrees≤θs2B−θs2A≤50 degrees and is preferably in the range 20degrees≤θs2B−θs2A≤40 degrees. In such a configuration, the inclinationangle θs 2B of the second short portion 412B having the large amplitudeAs2 is large, and thus the zigzag shape having the different amplitudesAs1 and As2 is formed. Accordingly, the rigidity of the center landportion 32 (33) can be increased in a region having the small amplitudeAs1 while the effect of improving drainage properties by the zigzagshape is ensured.

Note that the groove width Ws and the groove depth Hs of thecircumferential narrow groove 41 may be constant throughout the entirecircumference of the tire as described above or may be periodicallyincreased or decreased at a predetermined position. For example, thecircumferential narrow groove 41 can have a wide groove width (dimensionsymbol omitted in the drawings) and a shallow groove depth Hs′ (see FIG.6 ) in a region including the first short portion 412A having the zigzagshape, more specifically, in a region including a connection point ofeach of the first and second lateral grooves 42A, 42B described below.Meanwhile, the circumferential narrow groove 41 can have a narrow groovewidth (dimension symbol omitted in the drawings) and a deep groove depthHs (see FIG. 6 ) in a region including the second short portion 412Bhaving the zigzag shape. As a result, the groove volume of thecircumferential narrow groove 41 is ensured, and the wet performance ofthe tire is ensured. In addition, the rigidity of the center landportions 32, 33 is ensured, and uneven wear of the tire is suppressed.In this case, a ratio between the wide groove width and the narrowgroove width that are described above is preferably in the range of 1.0or larger and 2.0 or smaller. Further, the shallow groove depth Hs′described above is realized by the bottom upper portion 41′ formed at agroove bottom of the circumferential narrow groove 41. Furthermore, theshallow groove depth Hs′ is in the range 0.5 mm≤Hs′≤4.0 mm and is in therange 0.05≤Hs′/Hg1≤0.20 with respect to the groove depth Hg1 of theshoulder main groove 21.

As illustrated in FIG. 3 , the plurality of lateral grooves 42A, 42Binclude the first and second lateral grooves 42A, 42B. The first lateralgroove 42A opens to one edge portion of the center land portion 32; 33(the left side in the drawing) at one end and connects to thecircumferential narrow groove 41 at the other end. The second lateralgroove 42B opens to the other edge portion of the center land portion32; 33 (the right side in the drawing) at one end and connects to thecircumferential narrow groove 41 at the other end. Also, a set of thelateral grooves 42A, 42B is disposed at the same position in the tirecircumferential direction, and a plurality of sets of the lateralgrooves 42A, 42B are arranged at predetermined intervals in the tirecircumferential direction.

Additionally, in FIG. 4 , a pitch length P1 between the first lateralgrooves 42A with respect to the ground contact width Wb2 (Wb3) of thecenter land portion 32 (33) is in the range 0.50≤P1/Wb2≤1.10 and ispreferably in the range 0.75≤P1/Wb2≤0.95. With the lower limit describedabove, the effect of improving drainage properties by the lateralgrooves 42A, 42B is ensured. With the upper limit described above, therigidity of the center land portions 32, 33 is ensured. Note that in theconfiguration illustrated in FIG. 4 , the pitch length P1 between thefirst lateral grooves 42A is equal to the pitch length Ps of the zigzagshape of the circumferential narrow groove 41. Accordingly, the numberof waves having the zigzag shape of the circumferential narrow groove 41is twice the pitch number of the first lateral groove 42A.

Also, as illustrated in FIG. 4 , the first lateral grooves 42A and thesecond lateral grooves 42B alternately connect to the circumferentialnarrow groove 41 in the tire circumferential direction. Further, thefirst and second lateral grooves 42A, 42B respectively connect to thelong portions 411A, 411B having the zigzag shape of the circumferentialnarrow groove 41. Specifically, as illustrated in FIG. 4 , the firstlateral groove 42A connects to the first long portion 411A having thezigzag shape of the circumferential narrow groove 41 described above ina T-shape, and the second lateral groove 42B connects to the second longportion 411B in a T-shape. Furthermore, the lateral grooves 42A, 42Badjacent to each other in the tire width direction connect mutually tothe different long portions 411A, 411B. Accordingly, one short portion412A; 412B and a pair of end points thereof (a pair of bend pointshaving the zigzag shape) are disposed between the connection points ofthe adjacent lateral grooves 42A, 42B. Additionally, a pair of longportions 411A, 411B are disposed between the connection points of thelateral grooves 42A, 42A adjacent in the tire circumferential direction,and a pair of short portions 412A, 412B are disposed between theconnection points of the lateral grooves 42B, 42B adjacent in the tirecircumferential direction.

In the configuration described above, (1) the circumferential narrowgroove 41 has a zigzag shape in which long portions and short portionsare alternately connected, and the first and second lateral grooves 42A,42B connect mutually to the different long portions 411A, 411B from theleft and right of the circumferential narrow groove 41. Accordingly, thecircumferential narrow groove 41 includes the short portions 412A, 412Bhaving the zigzag shape, each of the short portions being disposedbetween the connection portions of the adjacent lateral grooves 42A,42B. As a result, drainage properties on the road contact surfaces ofthe center land portions 32, 33 are improved, and the wet performance ofthe tire is improved. Additionally, as compared with a configuration(not illustrated) where both the first and second lateral groovesconnect to one long portion from the left and right and a configuration(not illustrated) where the first and second lateral grooves connect tobend points having the zigzag shape, the rigidity of the center landportions 32, 33 is ensured, and the concentration of distortion on theedge portion defined by the lateral grooves 42A, 42B is relieved. Thus,uneven wear of the center land portions 32, 33 is suppressed. Thisprovides wet performance and uneven wear resistance performance of thetire in a compatible manner.

Also, as illustrated in FIG. 4 , the first and second lateral grooves42A, 42B are disposed near the first short portion 412A having the smallamplitude As1. As a result, as compared with a configuration (notillustrated) where the first and second lateral grooves 42A, 42B eachconnect to the region near the second short portion 412B having thelarge amplitude As2, the extension length in the tire width direction ofthe first and second lateral grooves 42A, 42B is ensured, and drainageproperties of the center land portions 32, 33 are improved.Specifically, in FIG. 5 , distances DL1, DL2 in the tire circumferentialdirection from the end points of the first short portion 412A to theconnection points of the first and second lateral grooves 42A, 42B withrespect to the pitch length Ps of the zigzag shape of thecircumferential narrow groove 41 are in the range of 3% or more and 20%or less and are preferably in the range of 5% or more and 15% or less.With the lower limit described above, the rigidity of the center landportions 32, 33 is ensured, and uneven wear of the center land portions32, 33 is suppressed. With the upper limit described above, the effectof improving drainage properties by the arrangement of the lateralgrooves 42A, 42B near the first short portion 412A is ensured.

Further, groove widths W1, W2 of the first and second lateral grooves42A, 42B are in the range 0.1 mm or more and 2.0 mm or less and arepreferably in the range of 0.5 mm or more and 1.5 mm or less. With thelower limit described above, drainage properties of the lateral grooves42A, 42B are ensured. With the upper limit described above, a decreasein rigidity of the center land portions 32, 33, which is caused by thearrangement of the lateral grooves 42A, 42B is suppressed. Furthermore,the groove widths W1, W2 of the lateral grooves 42A, 42B may be constantentirely along the lateral grooves 42A, 42B as described below, or maybe increased or decreased in a predetermined region.

Also, in FIG. 5 , each of the first and second lateral grooves 42A, 42Bincludes an inclined portion 421, an axial direction portion 422, and aconnection portion 423.

As illustrated in FIG. 5 , the inclined portion 421 is a groove portioninclined at a predetermined inclination angle ϕ21A, ϕ21B with respect tothe tire circumferential direction, and forms a central portion in alongitudinal direction of each of the lateral grooves 42A, 42B. Further,the inclined portions 421 of the first and second lateral grooves 42A,42B are inclined in the opposite direction to the long portions 411A,411B having the zigzag shape of the circumferential narrow groove 41 inthe tire circumferential direction. Accordingly, the rigidity balance ofthe center land portion 32 (33) is ensured. Furthermore, the inclinedportions 421 of the first and second lateral grooves 42A, 42B areinclined mutually in the same direction with respect to the tirecircumferential direction. In such a configuration, as compared with aconfiguration (not illustrated) where the first and second lateralgrooves are inclined in mutually opposite directions with respect to thetire circumferential direction, the rigidity balance of the center landportion 32 (33) is ensured, and strain energy on the center land portion32 (33) formed in a rib shape is dispersed. Thus, uneven wear resistanceperformance is improved. Additionally, the inclination angles ϕ21A, ϕ21Bof the inclined portions 421 are in the range of 40 degrees or more and80 degrees or less and are preferably in the range of 50 degrees or moreand 70 degrees or less. Moreover, the inclination angles ϕ21A, ϕ21B ofthe inclined portions 421 are substantially equal, and specifically, arein the range of −10 degrees≤ϕ21A−ϕ21B≤10 degrees.

Further, the first and second lateral grooves 42A, 42B have the maximumgroove widths W1, W2 (see FIG. 4 ) in the inclined portions 421.Furthermore, a groove depth H21 (FIG. 7 ) of the inclined portion 421 isin the range 0.5 mm≤H21≤4.0 mm and is in the range 0.05≤H21/Hg1≤0.15with respect to the groove width Hg1 of the shoulder main groove 21. Insuch a configuration, since the inclined portion 421 is a wide andshallow groove portion, drainage properties of the lateral grooves 42A,42B are ensured, and the rigidity of the center land portion 32 (33) isensured.

Also, in FIG. 5 , an extension length D21 in the tire width direction ofthe inclined portion 421 is in the range 0.10≤D21/Wb2≤0.50 with respectto the ground contact width Wb2 (Wb3) of the center land portion 32 (33)and is preferably in the range of 0.20≤D21/Wb2≤0.45, and is morepreferably in the range 0.24≤D21/Wb2≤0.40. With the lower limitdescribed above, the effect of improving drainage properties by theinclined portion 421 is ensured. With the upper limit described above, aspace for arranging in the tire width direction the axial directionportion 422 described below is ensured. Thus, uneven wear of the edgeportion of the center land portion 32 (33) is suppressed. Further, anextension length L21 in the tire circumferential direction of theinclined portion 421 with respect to the pitch length Ps of the zigzagshape of the circumferential narrow groove 41 is in the range0.10≤L21/Ps≤0.40 and is preferably in the range 0.20≤L21/Ps≤0.30. Withthe lower limit described above, the effect of improving drainageproperties by the inclined portion 421 is ensured. With the upper limitdescribed above, the rigidity of the center land portion 32 (33) isensured. Note that in the configuration of FIG. 5 , the extension lengthL21 in the tire circumferential direction of the inclined portion 421 isequal to an extension length L2 in the tire circumferential direction ofthe lateral grooves 42A, 42B.

Furthermore, in the configuration of FIG. 5 , the inclined portion 421has a straight shape, and thus the lateral grooves 42A, 42B have aZ-shape or a step shape. However, no such limitation is intended. Theinclined portion 421 has an arc shape or an S-shape, and thus thelateral grooves 42A, 42B may have a curved shape (not illustrated).

The axial direction portion 422 is a groove portion connecting theinclined portion 421 and the edge portion of the center land portion 32(33) and extends substantially parallel to the tire rotation axis andconnects to the edge portion of the center land portion 32 (33) in aT-shape. Additionally, the inclination angle (dimension symbol omittedin the drawings) of the axial direction portion 422 with respect to thetire circumferential direction is in the range of 80 degrees or more and110 degrees or less. In such a configuration, since the lateral grooves42A, 42B connect perpendicular to the edge portion of the center landportion 32 (33), the edge portion of the center land portion 32 (33) isprevented from being damaged from an opening portion of the lateralgrooves 42A, 42B.

Further, the groove width (dimension symbol omitted in the drawings) ofthe axial direction portion 422 is in the range of 0.1 mm or more and2.0 mm or less, is preferably in the range of 0.5 mm or more and 1.5 mmor less. Furthermore, preferably, the groove width of the axialdirection portion 422 is narrower than the groove width of the inclinedportion 421 and is in the range of 50% or more and less than 100% withrespect to the groove width of the inclined portion 421. Moreover, agroove depth H22 (see FIG. 7 ) of the axial direction portion 422 isdeeper than the groove depth H21 of the inclined portion 421 (H21<H22)and is in the range 0.60≤H21/Hg1≤0.80 with respect to the groove depthHg1 of the shoulder main groove 21. For example, in the configuration ofFIG. 5 , multisipes 5 described below serve as the axial directionportions 422 of the lateral grooves 42A, 42B, and thus the axialdirection portions 422 each have a depth equal to that of the multisipes5. However, no such limitation is intended. The axial direction portion422 may have the groove depth H21 equal to the depth of the inclinedportion 421, and thus the entire lateral grooves 42A, 42B may have ashallow groove structure (not illustrated).

In FIG. 5 , an extension length D22 in the tire width direction of theaxial direction portion 422 with respect to the ground contact width Wb2(Wb3) of the center land portion 32 (33) is in the range0.05≤D22/Wb2≤0.20 and is preferably in the range 0.10≤D22/Wb2≤0.15.Additionally, the extension length D22 of the axial direction portion422 is in the range 2.0 mm≤D22≤5.0 mm.

The connection portion 423 is a groove portion that connects theinclined portion 421 and the circumferential narrow groove 41. Theconnection portions 423 respectively connect in a T-shape to the longportions 411A, 411B having the zigzag shape of the circumferentialnarrow groove 41. Further, the inclination angle of the connectionportion 423 with respect to the tire circumferential direction is in therange of 80 degrees or more and 110 degrees or less.

Furthermore, the groove width (dimension symbol omitted in the drawings)of the connection portion 423 is in the range of 0.1 mm or more and 2.0mm or less and is preferably in the range 0.5 mm or more and 1.5 mm orless. Additionally, the groove depth (dimension symbol omitted in thedrawings, see FIG. 7 ) of the connection portion 423 has the groovedepth H21 equal to that of the inclined portion 421. Accordingly, thelateral grooves 42A, 42B each have a shallow groove depth at the openingportion with respect to the circumferential narrow groove 41.

Also, in FIG. 2 , the first center land portion 32 adjacent to one ofthe pair of shoulder land portions 31, 31 (for example, the shoulderland portion 31 on the left side in the drawing), the second center landportion 33 adjacent to the first center land portion 32, the thirdcenter land portion 32 adjacent to the other of the pair of shoulderland portions 31, 31 (for example, the shoulder land portion 31 on theright side in the drawing) are defined. In the configuration of FIG. 2 ,the first to third center land portions 32, 33, 32 each include thecircumferential narrow groove 41 and the first and second lateralgrooves 42A, 42B.

In this case, as illustrated in FIG. 3 , the first lateral groove 42Aand the second lateral groove 42B of the first center land portion 32are disposed overlapped with each other in the tire circumferentialdirection. Similarly, the first lateral groove 42A and the secondlateral groove 42B of the second center land portion 33 are disposedoverlapped with each other in the tire circumferential direction.Additionally, as illustrated in FIG. 2 , the first lateral groove 42Aand the second lateral groove 42B of the third center land portion 32are disposed overlapped with each other in the tire circumferentialdirection.

In the configuration described above, since the first lateral groove 42Aand the second lateral groove 42B are disposed overlapped with eachother in the tire circumferential direction in each of the first tothird center land portions 32, 33, 32, the concentration of distortionon the edge portions defined by the lateral grooves 42A, 42B isrelieved. Thus, uneven wear of the center land portions 32, 33 issuppressed as compared with a configuration (not illustrated) where thelateral grooves are disposed offset in the tire circumferentialdirection.

Moreover, an overlap amount DA (see FIG. 3 ) of the first and secondlateral grooves 42A and 42B in each of the first to third center landportions 32, 33, 32 with respect to the pitch length P1 (see FIG. 3 )between the first lateral grooves 42A is in the range 0.05≤DA/P1≤0.40and is preferably in the range 0.10≤DA/P1≤0.30. Accordingly, in onecenter land portion 32; 33, strains of the edge portions of the centerland portions 32, 33 due to overlapping of the lateral grooves 42A, 42Bwith each other are reduced.

The overlap amount DA between the lateral grooves 42A, 42B is measuredas an overlapping distance in the tire circumferential direction betweenthe first and second lateral grooves 42A, 42B when projected onto thetire equatorial plane CL.

Further, as illustrated in FIG. 3 , the first and second lateral grooves42A, 42B of the first center land portion 32 are disposed offset in thetire circumferential direction with respect to the first and secondlateral grooves 42A, 42B of the second center land portion 33.Furthermore, as illustrated in FIG. 2 , the first and second lateralgrooves 42A, 42B of the first center land portion 32, the first andsecond lateral grooves 42A, 42B of the second center land portion 33,and the first and second lateral grooves 42A, 42B of the third centerland portion 32 are disposed mutually offset in the tire circumferentialdirection.

In the configuration described above, the lateral grooves 42A, 42B ofthe adjacent center land portions 32, 33; 33, 32 are disposed mutuallyoffset in the tire circumferential direction. Accordingly, as comparedwith a configuration (not illustrated) where the lateral grooves aredisposed overlapped in the tire circumferential direction, periodicresonance caused by the lateral grooves 42A, 42B is canceled, and noiseduring traveling is reduced.

Further, an offset amount DB (see FIG. 3 ) between the first and secondlateral grooves 42A, 42B of the first center land portion 32 and thefirst and second lateral grooves 42A, 42B of the second center landportion 33 with respect to the pitch length P1 (see FIG. 3 ) between thefirst lateral grooves 42A is in the range 0.10≤DB/P1 and is preferablyin the range 0.15≤DB/P1. Accordingly, the noise reduction effect duringtraveling is ensured by mutual offset of the lateral grooves 42A, 42B ofthe adjacent center land portions 32, 33. The upper limit of a ratioDB/L2 is not particularly limited but is restricted in relation to thepitch length P1 (see FIG. 3 ) between the lateral grooves 42A because itis required that a pair of the adjacent lateral grooves 42A, 42B are notoverlapped with each other.

The offset amount DB of the lateral grooves 42A, 42B is measured as aseparation distance in the tire circumferential direction between thefirst and second lateral grooves 42A, 42B of the center land portion 32and the first and second lateral grooves 42A, 42B of the center landportion 33 adjacent to the center land portion 32 when projected ontothe tire equatorial plane CL.

Shoulder Land Portion

As illustrated in FIG. 2 , the shoulder land portion 31 is a rib havinga road contact surface continuous in the tire circumferential direction.Additionally, the shoulder land portion 31 includes only the multisipes5 and does not include other grooves or sipes. Accordingly, the shoulderland portion 31 includes a plain road contact surface that is notdivided in the tire circumferential direction by grooves or sipes. As aresult, uneven wear resistance of the shoulder land portion 31 whereuneven wear easily occurs can be improved. However, no such limitationis intended, and the shoulder land portion 31 may include shallow sipesor shallow grooves having a depth of 15 mm or less (not illustrated).

Multisipes

In the configuration of FIG. 2 , each of the land portions 31 to 33includes a plurality of multisipes 5. The multisipes 5 are each a shortsipe opening to the edge portion of the land portions 31 to 33 at oneend and terminating within the land portions 31 to 33 at the other end.The multisipes 5 each have a width of 0.3 mm or more and 1.5 mm or less(dimension symbol omitted in the drawings), a depth H5 (see FIG. 7 ) of2.0 mm or more and 17 mm or less, and a length of 2.0 mm or more and 10mm or less (dimension symbol omitted in the drawings, see FIG. 5 ).Additionally, the plurality of multisipes 5 are arranged in the tirecircumferential direction along the edge portions of the land portions31 to 33. Further, a pitch length (dimension symbol omitted in thedrawings) between the multisipes 5 with respect to the tirecircumferential length is in the range of 0.1% or more and 0.6% or less.In such a configuration, the rigidity of the land portions 31 to 33 isreduced by the multisipes 5, and thus ground contact pressure of theedge portions of the land portions 31 to 33 when the tire comes intocontact with the ground is reduced. As a result, the occurrence ofuneven wear (in particular, river wear) is suppressed, and uneven wearresistance performance of the tire is improved.

Note that, in the configuration of FIG. 2 , as illustrated in FIGS. 5and 7 , some of the multisipes 5 serve as the axial direction portions422 of the lateral grooves 42A, 42B of the center land portions 32, 33.As just described, the lateral grooves 42A, 42B are connected to themultisipes 5 and thus may open to the edge portions of the center landportions 32, 33. In this case, preferably, the multisipes 5 each have awidth narrower than the groove widths W1, W2 (see FIG. 4 ) of theinclined portions 421 of the lateral grooves 42A, 42B and have a depthH5 deeper than the groove depth H21 (see FIG. 7 ) of the inclinedportions 421 of the lateral grooves 42A, 42B. As a result, the drainagefunction by the lateral grooves 42A, 42B and the effect of suppressinguneven wear by the multisipes 5 are provided in a compatible manner.

Wear Sacrifice Rib

FIG. 8 is a cross-sectional view illustrating the edge portion of theshoulder land portion 31 illustrated in FIG. 2 .

As illustrated in FIGS. 2 and 8 , the shoulder land portion 31 includesa narrow groove 61 that extends along the edge portion on the tireground contact edge T side, and a narrow rib 62 defined by the narrowgroove 61. Additionally, a groove width W6 of the narrow groove 61 is inthe range 1.0 mm≤W6≤3.0 mm, and a groove depth H6 of the narrow groove61 with respect to the groove depth Hg1 of the shoulder main groove 21(see FIG. 6 ) is in the range 0.60≤H6/Hg1≤1.00. In such a configuration,the narrow rib 62 functions as a so-called wear sacrifice rib duringrolling of the tire and suppresses uneven wear of the body of theshoulder land portion 31. As a result, the uneven wear resistanceperformance of the tire is improved.

Further, in the configuration of FIG. 8 , the narrow groove 61 has awidened portion having a circular cross-section (reference sign omittedin drawings) at the groove bottom. Furthermore, a diameter of thewidened portion with respect to the groove width W6 of the narrow groove61 is in the range of 1.2 times or more and 5 times or less.Additionally, the top surface of the narrow rib 62 is disposed offset inthe tire radial direction with respect to the road contact surface ofthe shoulder land portion 31. Additionally, an offset amount D6 of thetop surface of the narrow rib 62 is in the range 1.0 mm≤D6≤4.0 mm.Moreover, the width (dimension symbol omitted in drawings) of the topsurface of the narrow rib 62 with respect to the ground contact widthWb1 of the shoulder land portion 31 (see FIG. 2 ) is in the range of 20%or more and 40% or less. As a result, the effect of suppressing unevenwear by the wear sacrifice rib is improved.

Modified Examples

FIG. 9 is a plan view illustrating a modified example of the tire 1illustrated in FIG. 2 . In the same drawing, constituents identical tothose in FIG. 2 have identical reference signs, and descriptions thereofwill be omitted.

In the configuration of FIG. 2 , the groove width Wg2 of the center maingroove 22 is set to be equal to or slightly smaller than the groovewidth Wg1 of the shoulder main groove 21. Specifically, the groove widthWg2 of the center main groove 22 with respect to the groove width Wg1 ofthe shoulder main groove 21 is in the range 0.70≤Wg2/Wg1≤1.00 and ispreferably in the range 0.80≤Wg2/Wg1≤0.90. Accordingly, the groove widthWg2 of the center main groove 22 is set to be equal to or slightlynarrower than the groove width Wg1 of the shoulder main groove 21. As aresult, drainage properties of the tread portion center region areensured. In such a configuration, preferably, the drainage properties ofthe tread portion center region are improved and thus the wetperformance of the tire is improved.

In contrast, in the configuration of FIG. 9 , the groove width Wg2 ofthe center main groove 22 is narrower than the groove width Wg1 of theshoulder main groove 21 and is in the range 0.14≤Wg2/Wg1≤0.45.Additionally, the groove width Wg2 of the center main groove 22 is inthe range 3.5 mm≤Wg2≤6.0 mm. In such a configuration, the rigidity ofthe tread portion center region is increased, and the uneven wearresistance performance of the tire is improved. Also, the rollingresistance performance of the tire is improved.

Effect

As described above, the tire 1 includes a pair of shoulder main grooves21 and one or more center main grooves 22, and a pair of shoulder landportions 31 and two or more center land portions 32, 33 defined andformed by the shoulder main grooves 21 and the center main grooves 22(see FIG. 2 ). Additionally, of the two or more center land portions 32,33, the first center land portion 32 adjacent to the shoulder landportion 31 and the second center land portion 33 adjacent to the firstcenter land portion 32 are defined. In this case, the first and secondcenter land portions 32, 33 each include the circumferential narrowgroove 41 extending in the tire circumferential direction, and the firstlateral groove 42A opening to one edge portion of each of the centerland portions 32, 33 at one end and connecting to the circumferentialnarrow groove 41 at the other end, and the second lateral groove 42Bopening to the other edge portion of each of the center land portions32, 33 at one end and connecting at the other end to the circumferentialnarrow groove 41 at the other end. Further, the first and second lateralgrooves 42A, 42B of the first center land portion 32 are disposedoverlapped with each other in the tire circumferential direction (seeFIG. 3 ). Furthermore, the first and second lateral grooves 42A, 42B ofthe second center land portion 33 are disposed overlapped with eachother in the tire circumferential direction. In addition, the first andsecond lateral grooves 42A, 42B of the first center land portion 32 aredisposed offset in the tire circumferential direction with respect tothe first and second lateral grooves 42A, 42B of the second center landportion 33.

In such a configuration, (1) the first and second center land portions32, 33 each include the circumferential narrow groove 41 and the lateralgrooves 42A, 42B, improving drainage properties of the tread portioncenter region. Further, (2) the first lateral groove 42A and the secondlateral groove 42B are disposed overlapped with each other in the tirecircumferential direction in each of the first and second center landportions 32, 33. Accordingly, as compared with a configuration (see FIG.12 described below) where the lateral grooves are disposed offset in thetire circumferential direction, the concentration of distortion on theedge portions defined by the lateral grooves 42A, 42B is relieved, anduneven wear of the center land portions 32, 33 is suppressed.Furthermore, (3) the lateral grooves 42A, 42B of the adjacent centerland portions 32, 33 are disposed mutually offset in the tirecircumferential direction. Accordingly, as compared with a configuration(see FIG. 12 described below) where the lateral grooves of the adjacentcenter land portions are disposed overlapped in the tire circumferentialdirection, periodic resonance caused by the lateral grooves 42A, 42B iscanceled, and noise during traveling is reduced. This has the advantageof providing wet performance, uneven wear resistance performance, andnoise performance in a compatible manner.

Additionally, an overlap amount DA (see FIG. 3 ) of the first and secondlateral grooves 42A, 42B in each of the first and second center landportions 32, 33 with respect to the pitch length P1 (see FIG. 3 )between the first lateral grooves 42A is in the range 0.05≤DA/P1≤0.40.The lower limit described above has an advantage of reducing strains ofthe edge portions of the center land portion 32, 33 due to overlappingof the lateral grooves 42A, 42B of the single center land portion 32, 33with each other.

Moreover, in the tire 1, an offset amount DB (see FIG. 3 ) between thefirst and second lateral grooves 42A, 42B of the first center landportion 32 and the first and second lateral grooves 42A, 42B of thesecond center land portion 33 with respect to the pitch length P1 (seeFIG. 3 ) between the first lateral grooves 42A is in the range0.10≤DB/P1. This has an advantage of ensuring the noise reduction effectduring traveling by mutual offset between the lateral grooves 42A, 42Bof the adjacent center land portions 32, 33.

Further, in the tire 1, each of the first and second lateral grooves42A, 42B of the first and second center land portions 32, 33 includesthe inclined portion 421 inclined with respect to the tirecircumferential direction (see FIG. 5 ). Furthermore, the inclinationangle ϕ21A, ϕ21B of the inclined portion 421 is in the range of 40degrees or more and 80 degrees or less. Additionally, the inclinedportions 421 of the first and second lateral grooves 42A, 42B areinclined mutually in the same direction with respect to the tirecircumferential direction. In such a configuration, there is anadvantage that as compared with a configuration (not illustrated) wherethe first and second lateral grooves are inclined in mutually oppositedirections with respect to the tire circumferential direction, therigidity balance of the center land portion 32 (33) is ensured, andstrain energy on the center land portion 32 (33) formed in a rib shapeis dispersed and thus uneven wear resistance performance is improved.

Moreover, in the tire 1, the groove depth H21 of the inclined portion421 with respect to the groove depth Hg1 of the shoulder main groove 21is in the range 0.05≤H21/Hg1≤0.15 (see FIG. 7 ). There is an advantagethat with the lower limit described above, drainage properties of thelateral grooves 42A, 42B are ensured, and there is an advantage thatwith the upper limit described above, the rigidity of the center landportion 32 (33) is ensured.

Additionally, in the tire 1, the extension length D21 in the tire widthdirection of the inclined portion 421 of each of the first and secondlateral grooves 42A, 42B with respect to the ground contact width Wb2 ofthe center land portion 32 (33) is in the range 0.10≤D21/Wb2≤0.50 (seeFIG. 5 ). The lower limit described above has an advantage of ensuringthe effect of improving drainage properties by the inclined portion 421,and the upper limit described above has an advantage of ensuring thearrangement space of the axial direction portion 422 in the tire widthdirection.

Additionally, in the tire 1, each of the first and second lateralgrooves 42A, 42B includes the axial direction portion 422 connecting theinclined portion 421 and the edge portion of the center land portion 32(33) (see FIG. 5 ). Moreover, the inclination angle (dimension symbolomitted in the drawings) of the axial direction portion 422 with respectto the tire circumferential direction is in the range of 80 degrees ormore and 110 degrees or less. In such a configuration, there is anadvantage that since the lateral grooves 42A, 42B each connectperpendicularly to the edge portion of the center land portion, afailure of the edge portion of the center land portion 32 (33) from theopening portion of the lateral groove 42A, 42B is suppressed.

Further, in the tire 1, the extension length D22 in the tire widthdirection of the axial direction portion 422 with respect to the groundcontact width Wb2 (Wb3) of the center land portion 32 (33) is in therange 0.05≤D22/Wb2≤0.20. Accordingly, there is an advantage that theextension length of the axial direction portion 422 is properly set.

Furthermore, in the tire 1, the circumferential narrow groove 41 has azigzag shape formed by alternately connecting the long portions 411A,411B and the short portions 412A, 412B (see FIGS. 3 and 4 ).Accordingly, there is an advantage of improving wet performance of thetire compared with a configuration (not illustrated) where thecircumferential narrow groove has a straight shape.

Additionally, in the tire 1, the shoulder land portion 31 includes aplain road contact surface that is not divided in the tirecircumferential direction by grooves or sipes (see FIG. 2 ).Accordingly, there is an advantage that uneven wear resistance of theshoulder land portion 31 where uneven wear easily occurs can beimproved.

Further, the tire 1 includes three or more center land portions 32, 33,32 (see FIG. 2 ). Furthermore, of the three or more center land portions32, 33, 32, the first center land portion 32 adjacent to one of the pairof shoulder land portions 31, 31, the second center land portion 33adjacent to the first center land portion 32, and the third center landportion 32 adjacent to the other of the pair of shoulder land portions31, 31 are defined. In this case, the third center land portion 32includes the circumferential narrow groove 41 extending in the tirecircumferential direction, the first lateral grooves 42A each opening atone end to one edge portion of the third center land portion 32 andconnecting at the other end to the circumferential narrow groove 41, andthe second lateral grooves 42B each opening at one end to the other edgeportion of the third center land portion 32 and connecting at the otherend to the circumferential narrow groove 41. Additionally, the first andsecond lateral grooves 42A, 42B of the third center land portion 32 aredisposed overlapped with each other in the tire circumferentialdirection. The first and second lateral grooves 42A, 42B of the firstcenter land portion 32, the first and second lateral grooves 42A, 42B ofthe second center land portion 33, and the first and second lateralgrooves 42A, 42B of the third center land portion 32 are disposedmutually offset in the tire circumferential direction. Accordingly,there is an advantage that periodic resonance caused by the lateralgrooves 42A, 42B of the three or more center land portions 32, 33, 32 iscanceled and thus noise during traveling is reduced.

Additionally, in the tire 1, the plurality of circumferential maingrooves 21, 22 includes a pair of shoulder main grooves 21 and one ormore center main grooves 22, and the groove width Wg2 of the center maingroove 22 is narrower than the groove width Wg1 of the shoulder maingroove 21 (Wg2≤Wg1) (see FIG. 2 ). Accordingly, there is an advantagethat the rigidity of the tread portion center region is increased andthus rolling resistance performance of the tire is improved.

Target of Application

Additionally, the tire 1 is a heavy duty tire mounted on a steering axleof a vehicle. Therefore, by applying the technology to such a heavy dutytire, the effect of improving the tire performances described above iseffectively obtained.

Additionally, in the embodiments, a pneumatic tire is described as anexample of the tire. However, no such limitation is intended, and theconfigurations described in the embodiments can also be applied to othertires in a discretionary manner within the scope of obviousness to oneskilled in the art. Examples of other tires include an airless tire, anda solid tire.

Examples

FIGS. 10 and 11 are tables indicating the results of performance testsof tires according to embodiments of the technology. FIG. 12 is a planview illustrating a tread surface of a tire of Conventional Example.

In the performance tests, a plurality of types of test tires wasevaluated in terms of (1) wet braking performance, (2) uneven wearresistance performance, and (3) noise performance. Further, test tireshaving a tire size of 295/75R22.5 are assembled on rims specified by TRAand specified internal pressure and specified load by TRA are applied tothe test tires. Furthermore, the test tires are mounted on a 2-D tractorhead that is a test vehicle.

i) In the evaluation of wet braking performance, the test vehicletravels on an asphalt road on which water is sprinkled to a water depthof 1 mm, and a braking distance from an initial speed of 40 km/h ismeasured. Evaluation was carried out by expressing the measurementresults as index values with the results of Conventional Example beingdefined as the reference (100). In the evaluation, larger values arepreferable.ii) In the evaluation of uneven wear resistance performance, after thetest vehicle travels 50,000 km on a predetermined paved road, the depthof step wear of the edge portion of the land portion is observed and isexpressed as index values and evaluated. The evaluation is expressed asindex values with the value of Conventional Example being assigned thereference (100). In the evaluation, larger values are preferable.iii) In the evaluation of noise performance, pass-by noise (vehicleexternal noise) of the vehicle is measured under test conditionscompliant with R117-2 (Regulation No. 117 Revision 2) of ECE (EconomicCommission for Europe). Then, on the basis of the measurement results,the evaluation is expressed as index values with the value ofConventional Example being assigned the reference (100). In theevaluation, larger values are preferable.

The test tires of Examples 1 to 20 each include the configurations ofFIGS. 1 and 2 , and each test tire includes four circumferential maingrooves 21, 22, a pair of shoulder land portions 31, and three centerland portions 32, 33. Further, all of the center land portions 32, 33each include the circumferential narrow groove 41 formed by connectingthe long portions 411A, 411B and the short portions 412A, 412B, and thelateral grooves 42A, 42B connecting to the long portions 411A, 411B ofthe circumferential narrow groove 41. Furthermore, the first and secondshort portions 412A, 412B of the circumferential narrow groove 41 havelengths different from each other. Additionally, the lateral grooves42A, 42B are arranged in a staggered manner in the tire circumferentialdirection, and alternately connect to the long portions 411A, 411B ofthe circumferential narrow groove 41 having a zigzag shape. Further, thegroove width Wg1 of the shoulder main groove 21 is 10.5 mm, and thegroove depth Hg1 of the shoulder main groove 21 is 14.6 mm. Furthermore,the groove width Wg2 of the center main groove 22 is 9.0 mm, and thegroove depth Hg2 of the center main groove 22 is 12.9 mm. Additionally,the tire ground contact width TW is 212 mm, the ground contact width Wb1of the shoulder land portion 31 is 39.5 mm, and the ground contactwidths Wb2, Wb3 of the center land portions 32, 33 are 31.0 mm and 32.0mm. Moreover, the groove width Ws of the circumferential narrow groove41 is 0.7 mm, and the groove depth Hs of the circumferential narrowgroove 41 is 9.2 mm. In addition, the test tire of Example 21 has theconfiguration of FIG. 9 , and is identical to the test tire of Example 1except that the groove width Wg2 of the center main groove 22 is 4.6 mm,the tire ground contact width TW is 207 mm, and the ground contact widthWb1 of the shoulder land portion 31 is 41.4 mm.

In the test tire of Conventional Example, the number of waves having thezigzag shape of the circumferential narrow groove 41 is equal to thepitch number of the first lateral groove 42A in the test tire of Example1 (see FIG. 12 ). Accordingly, the adjacent first lateral grooves 42A,42A are connected by a set of a long portion and a short portion.Further, the lateral grooves 42A, 42B are arranged in a staggered mannerin the tire circumferential direction, and alternately connect to thebend points of the circumferential narrow groove 41 having a zigzagshape. Furthermore, the adjacent lateral grooves 42A, 42B are disposedmutually offset in the tire circumferential direction. Additionally, thelateral grooves 42A, 42B of the adjacent center land portions 32, 33 aredisposed overlapped with each other in the tire circumferentialdirection.

As can be seen from the test results, the test tires of Examples providewet braking performance, uneven wear resistance performance, and noiseperformance in a compatible manner.

What is claimed is:
 1. A tire, comprising: a pair of shoulder maingrooves and one or more center main grooves; and a pair of shoulder landportions and two or more center land portions defined and formed by theshoulder main grooves and the center main grooves; of the two or morecenter land portions, a first center land portion adjacent to a shoulderland portion of the pair of shoulder land portions and a second centerland portion adjacent to the first center land portion being defined,the first and second center land portions each comprising: acircumferential narrow groove extending in a tire circumferentialdirection; a first lateral groove opening to one edge portion of thecenter land portion at one end and connecting to the circumferentialnarrow groove at the other end; and a second lateral groove opening tothe other edge portion of the center land portion at one end andconnecting to the circumferential narrow groove at the other end; thefirst and second lateral grooves of the first center land portion beingdisposed overlapped with each other in the tire circumferentialdirection, the first and second lateral grooves of the second centerland portion being disposed overlapped with each other in the tirecircumferential direction, and the first and second lateral grooves ofthe first center land portion being disposed offset with respect to thefirst and second lateral grooves of the second center land portion inthe tire circumferential direction.
 2. The tire according to claim 1,wherein an overlap amount DA of the first and second lateral grooves ineach of the first and second center land portions with respect to apitch length P1 between the first lateral grooves is in a range0.05≤DA/P1≤0.40.
 3. The tire according to claim 1, wherein an offsetamount DB between the first and second lateral grooves of the firstcenter land portion and the first and second lateral grooves of thesecond center land portion with respect to a pitch length P1 between thefirst lateral grooves is in a range 0.10≤DB/P1.
 4. The tire according toclaim 1, wherein each of the first and second lateral grooves of thefirst and second center land portions comprises an inclined portioninclined with respect to the tire circumferential direction, aninclination angle of the inclined portion is in a range of 40 degrees ormore and 80 degrees or less, and the inclined portions of the first andsecond lateral grooves are inclined mutually in the same direction withrespect to the tire circumferential direction.
 5. The tire according toclaim 4, wherein a groove depth H21 of the inclined portion with respectto a groove depth Hg1 of the shoulder main groove is in a range0.05≤H21/Hg1≤0.15.
 6. The tire according to claim 5, wherein anextension length D21 of the inclined portion of each of the first andsecond lateral grooves in a tire width direction with respect to aground contact width Wb2 of the center land portion is in a range0.10≤D21/Wb2≤0.50.
 7. The tire according to claim 5, wherein each of thefirst and second lateral grooves comprises an axial direction portionconnecting the inclined portion to an edge portion of the center landportion, and an inclination angle of the axial direction portion withrespect to the tire circumferential direction is in a range of 80degrees or more and 110 degrees or less.
 8. The tire according to claim7, wherein an extension length D22 of the axial direction portion in thetire width direction with respect to the ground contact width Wb2 of thecenter land portion is in a range 0.05≤D22/Wb2≤0.20.
 9. The tireaccording to claim 1, wherein the circumferential narrow groove has azigzag shape formed by alternately connecting a long portion and a shortportion.
 10. The tire according to claim 1, wherein the shoulder landportion comprises a plain road contact surface that is not divided by agroove or a sipe in the tire circumferential direction.
 11. The tireaccording to claim 1, further comprising three or more of the centerland portions, of the three or more of the center land portions, thefirst center land portion adjacent to one of the pair of shoulder landportions, the second center land portion adjacent to the first centerland portion, and a third center land portion adjacent to the other ofthe pair of shoulder land portions being defined, the third center landportion comprising: a circumferential narrow groove extending in thetire circumferential direction; a first lateral groove opening to oneedge portion of the third center land portion at one end and connectingto the circumferential narrow groove at the other end; and a secondlateral groove opening to the other edge portion of the third centerland portion at one end and connecting to the circumferential narrowgroove at the other end; the first and second lateral grooves of thethird center land portion being disposed overlapped with each other inthe tire circumferential direction, and the first and second lateralgrooves of the first center land portion, the first and second lateralgrooves of the second center land portion, and the first and secondlateral grooves of the third center land portion being disposed mutuallyoffset in the tire circumferential direction.
 12. The tire according toclaim 1, wherein a plurality of circumferential main grooves comprises apair of shoulder main grooves and one or more center main grooves, and agroove width of each of the one or more center main grooves is narrowerthan a groove width of each of the pair of the shoulder main grooves.13. The tire according to claim 3, wherein each of the first and secondlateral grooves of the first and second center land portions comprisesan inclined portion inclined with respect to the tire circumferentialdirection, an inclination angle of the inclined portion is in a range of40 degrees or more and 80 degrees or less, and the inclined portions ofthe first and second lateral grooves are inclined mutually in the samedirection with respect to the tire circumferential direction.
 14. Thetire according to claim 13, wherein a groove depth H21 of the inclinedportion with respect to a groove depth Hg1 of the shoulder main grooveis in a range 0.05≤H21/Hg1≤0.15.
 15. The tire according to claim 14,wherein an extension length D21 of the inclined portion of each of thefirst and second lateral grooves in a tire width direction with respectto a ground contact width Wb2 of the center land portion is in a range0.10≤D21/Wb2≤0.50.
 16. The tire according to claim 15, wherein each ofthe first and second lateral grooves comprises an axial directionportion connecting the inclined portion to an edge portion of the centerland portion, and an inclination angle of the axial direction portionwith respect to the tire circumferential direction is in a range of 80degrees or more and 110 degrees or less.
 17. The tire according to claim16, wherein an extension length D22 of the axial direction portion inthe tire width direction with respect to the ground contact width Wb2 ofthe center land portion is in a range 0.05≤D22/Wb2≤0.20.
 18. The tireaccording to claim 17, wherein the circumferential narrow groove has azigzag shape formed by alternately connecting a long portion and a shortportion.
 19. The tire according to claim 18, wherein the shoulder landportion comprises a plain road contact surface that is not divided by agroove or a sipe in the tire circumferential direction.
 20. The tireaccording to claim 19, further comprising three or more of the centerland portions, of the three or more of the center land portions, thefirst center land portion adjacent to one of the pair of shoulder landportions, the second center land portion adjacent to the first centerland portion, and a third center land portion adjacent to the other ofthe pair of shoulder land portions being defined, the third center landportion comprising: a circumferential narrow groove extending in thetire circumferential direction; a first lateral groove opening to oneedge portion of the third center land portion at one end and connectingto the circumferential narrow groove at the other end; and a secondlateral groove opening to the other edge portion of the third centerland portion at one end and connecting to the circumferential narrowgroove at the other end; the first and second lateral grooves of thethird center land portion being disposed overlapped with each other inthe tire circumferential direction, and the first and second lateralgrooves of the first center land portion, the first and second lateralgrooves of the second center land portion, and the first and secondlateral grooves of the third center land portion being disposed mutuallyoffset in the tire circumferential direction.